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Science Final Exam Practice Unit 4 Short ANSWERS
50. What is the difference between extrusive rock and intrusive rock?
Extrusive rock is an igneous rock that forms when lava cools on the Earth’s
surface. Intrusive rock is an igneous rock that forms when magma cools and
hardens below the Earth’s surface. The time it takes for lava or magma to cool
determines the size of crystals in the rock, or whether crystals form at all. The
longer it takes for an extrusive or intrusive rock to cool, the larger the crystals will
be.
Granite, for example, is an intrusive igneous rock that takes a long time to cool
below the Earth’s surface. It’s crystals are much bigger than say basalt, an
extrusive rock which cools a little faster. Obsidian, an extrusive igneous rock,
cools rather quickly and has no crystals visible. It is a smooth, black glass type
of rock.
51. What is pumice? Explain why pumice floats.
Pumice is a volcanic rock (so igneous) that floats. Pumice forms when gases
cause the lava to foam up. The rock hardens quickly before the bubbles in the
foam disappear. Pumice is very porous (tiny holes) and lightweight which is why
it floats. It is the only rock that floats.
52. What is the difference between a rock and a mineral?
A mineral is a pure, naturally occurring, inorganic(non-living), solid substance
where as a rock is a mixture of two or more minerals.
53. Briefly explain how magma is different from lava.
Magma is molten material found BELOW Earth’s surface, where temperatures
and pressures are high. Lava is molten material that breaks THROUGH Earth’s
surface in the form of a volcanic eruption.
Magma - below the Earth’s surface
Lava - on the Earth’s surface
54. What do scientists now think is causing Earth’s plates to move?
Scientists now think that convection currents in the mantle, under Earth’s crust,
are causing Earth’s plates to move.
As we learned in Unit 2 on Heat, hot liquids/gases
tend to rise and cool liquids/gases tend to sink,
creating convection currents. The same process
might be occurring in Earth’s mantle. Hot magma
in the lower mantle moves upward after it is heated
by the intent heat in Earth’s core. At the upper part
of the mantle, the heated rock moves horizontally
under the plate about it, taking the plate along as if
the plate were on a conveyer belt.
55. Describe the three types of plate boundaries.
Convergent boundaries - plates that push/move towards each other.
Divergent boundaries - plates that pull/move away from each other.
Transform boundaries - plates that simply slide past each other without pushing
together or pulling apart.
* know how to draw the diagrams (drawn in class the last two days!)
56. Who proposed the Continental Drift theory? What evidence did he have
to support it?
Alfred Wegener proposed the Continental Drift theory. He found four different
types of evidence to support his ideas.
1. First he noticed something interesting about the shape of the continents. He
suggested that at one point all of the continents were once joined together in
a huge land mass called Pangaea. He thought they fit together, similar to a
puzzle.
2. He learned that fossils of the same animals were found on different
continents. For example, some fossils found in the Avalon Peninsula in
Newfoundland are very similar to those found in Wales, a country located
across the Atlantic Ocean from Newfoundland.
3. He discovered that geologists and found similarities in the rocks on both
sides of the Atlantic Ocean. The ages of rocks and rock layers in easter
North America and in Britain and Norway are the same!
4. And last but not least, climate change! Wegener noticed that some places
that have warm climates now, such as Africa, India, and Australia, have
evidence that they were once partly covered by glaciers.
Remember scientists have moved from the idea of continental drift to plate
tectonics.